Using Spring Data to access MongoDB

Spring Data is the data access Spring project for integrating with data stores. This post will cover the Spring Data sub project for accessing the document store MongoDB. It follows on from the Morphia post by showing how Spring Data for MongoDB would persist and query the same POJOs.

The four domain objects are shown below:

package com.city81.mongodb.springdata.entity;

import org.springframework.data.annotation.Id;

public abstract class BaseEntity {

 @Id
 protected String id;
 private Long version;

 public BaseEntity() {
  super();
 }

 public String getId() {
  return id;
 }

 public void setId(String id) {
  this.id = id;
 }

 public Long getVersion() {
  return version;
 }

 public void setVersion(Long version) {
  this.version = version;
 }

}

package com.city81.mongodb.springdata.entity;

import java.util.List;

import org.springframework.data.mongodb.core.mapping.Document;

@Document
public class Customer extends BaseEntity {

 private String name;
 private List<Account> accounts;
 private Address address;
 
 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 } 
  
 public List<Account> getAccounts() {
  return accounts;
 }

 public void setAccounts(List<Account> accounts) {
  this.accounts = accounts;
 }

 public Address getAddress() {
  return address;
 }

 public void setAddress(Address address) {
  this.address = address;
 }
 
}

package com.city81.mongodb.springdata.entity;


public class Address {

 private String number;
 private String street;
 private String town;
 private String postcode;
 
 public String getNumber() {
  return number;
 }
 public void setNumber(String number) {
  this.number = number;
 }
 public String getStreet() {
  return street;
 }
 public void setStreet(String street) {
  this.street = street;
 }
 public String getTown() {
  return town;
 }
 public void setTown(String town) {
  this.town = town;
 }
 public String getPostcode() {
  return postcode;
 }
 public void setPostcode(String postcode) {
  this.postcode = postcode;
 }
}

package com.city81.mongodb.springdata.entity;

import org.springframework.data.mongodb.core.mapping.Document;

@Document
public class Account extends BaseEntity {

 private String accountName;
 
 public String getAccountName() {
  return accountName;
 }

 public void setAccountName(String accountName) {
  this.accountName = accountName;
 }

}

Some classes are marked with the @Document annotation. This is optional but does allow you to provide a collection name eg

@Document(collection="personalBanking")

Also in the Customer class, the Address and Accounts attributes would be stored as embedded within the document but they can be stored separately by marking the variables with @DBRef. These objects will then be eagerly loaded when the Customer record is retrieved.

Next, using XML based metadata to register a MongoDB instance and a MongoTemplate instance.

The MongoFactoryBean is used to register an instance of com.mongodb.Mongo. Using the Bean as opposed to creating an instance of Mongo itself ensures that the calling code doesn't have to handle the checked exception UnknownHostException. It also ensures database specific exceptions are translated to be Spring exceptions of the DataAccessException hierarchy.

The MongoTemplate provides the operations (via the MongoOperations interface) to interact with MongoDB documents. This thread safe class has several constructors but for this example we only need to call the one that takes an instance of Mongo and the database name.

Whilst you could call the operations on the MongoTemplate to manage the entities, there exists a MongoRepository interface which can be extended to be 'document' specific via the use of Generics. The <mongo:repositories base-package="com.city81.mongodb.springdata.dao" />   registers beans extending this interface.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xmlns:context="http://www.springframework.org/schema/context"
 xmlns:mongo="http://www.springframework.org/schema/data/mongo" 
 xsi:schemaLocation="http://www.springframework.org/schema/beans        
  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd         
  http://www.springframework.org/schema/context         
  http://www.springframework.org/schema/context/spring-context-3.0.xsd
  http://www.springframework.org/schema/data/mongo 
  http://www.springframework.org/schema/data/mongo/spring-mongo.xsd">    
  
 <context:annotation-config />
  
 <context:component-scan base-package="com.city81.mongodb.springdata" />
 
 <!-- MongoFactoryBean instance --> 
 <bean id="mongo" class="org.springframework.data.mongodb.core.MongoFactoryBean">
  <property name="host" value="localhost" />
 </bean>   
 
 <!-- MongoTemplate instance --> 
 <bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
  <constructor-arg name="mongo" ref="mongo" />
  <constructor-arg name="databaseName" value="bank" />
 </bean> 
 
 <mongo:repositories base-package="com.city81.mongodb.springdata.dao" />
  
</beans>

The repository class in this example is the CustomerRepository. It gets wired with the MongoTemplate so provides the same (this time implicit type safe) operations but also provides the ability to add other methods. In this example, a find method has been added to demonstrate how a query can be built from the method name itself. There is no need to implement this method as Spring Data will parse the method name and determine the criteria ie findByNameAndAddressNumberAndAccountsAccountName will return documents where the customer name is equal to the first arg (name), and where the customer address number is equal to the second arg (number) and where the customer has an account which has an account name equal to the thrid arg (accountName).

package com.city81.mongodb.springdata.dao;

import java.util.List;

import org.springframework.data.mongodb.repository.MongoRepository;
import org.springframework.stereotype.Repository;

import com.city81.mongodb.springdata.entity.Customer;

@Repository
public interface CustomerRepository extends MongoRepository<Customer,String> {
 
 List<Customer> findByNameAndAddressNumberAndAccountsAccountName(
   String name, String number, String accountName);
 
}

In this example, we'll add a service layer in the form of the CustomerService class, which for this simple example just wraps the repository calls. The class has the CustomerRepository wired in and this service class is then in turn called from the Example class, which performs similar logic to the Morphia Example class.

package com.city81.mongodb.springdata.dao;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.city81.mongodb.springdata.entity.Customer;

@Service
public class CustomerService {  

 @Autowired
 CustomerRepository customerRepository;
  
 public void insertCustomer(Customer customer) {    
  customerRepository.save(customer);
 }
 
 public List<Customer> findAllCustomers() {           
  return customerRepository.findAll();
 }       
 
 public void dropCustomerCollection() {        
  customerRepository.deleteAll();   
 } 
 
 public List<Customer> findSpecificCustomers(
   String name, String number, String accountName) {           
  return customerRepository.findByNameAndAddressNumberAndAccountsAccountName(
    name, number, accountName);
 } 
 
}

package com.city81.mongodb.springdata;

import java.util.ArrayList;
import java.util.List;

import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.city81.mongodb.springdata.dao.CustomerService;
import com.city81.mongodb.springdata.entity.Account;
import com.city81.mongodb.springdata.entity.Address;
import com.city81.mongodb.springdata.entity.Customer;

public class Example {
 
 public static void main( String[] args ) {     
  
  ConfigurableApplicationContext context
   = new ClassPathXmlApplicationContext("spring/applicationContext.xml");       
  
  CustomerService customerService = context.getBean(CustomerService.class);       
  
  // delete all Customer records
  customerService.dropCustomerCollection();  
  
     Address address = new Address();
     address.setNumber("81");
     address.setStreet("Mongo Street");
     address.setTown("City");
     address.setPostcode("CT81 1DB");
    
     Account account = new Account();
     account.setAccountName("Personal Account");
     List<Account> accounts = new ArrayList<Account>();
     accounts.add(account);
     
     Customer customer = new Customer();
     customer.setAddress(address);
     customer.setName("Mr Bank Customer");
     customer.setAccounts(accounts);
          
     // insert a Customer record into the database
  customerService.insertCustomer(customer);          
     
     address = new Address();
     address.setNumber("101");
     address.setStreet("Mongo Road");
     address.setTown("Town");
     address.setPostcode("TT10 5DB");
    
     account = new Account();
     account.setAccountName("Business Account");
     accounts = new ArrayList<Account>();
     accounts.add(account);
     
     customer = new Customer();
     customer.setAddress(address);
     customer.setName("Mr Customer");
     customer.setAccounts(accounts);  

     // insert a Customer record into the database
  customerService.insertCustomer(customer);     
      
  // find all Customer records
  System.out.println("\nALL CUSTOMERS:");
  List<Customer> allCustomers = customerService.findAllCustomers();     
  for (Customer foundCustomer : allCustomers) {
   System.out.println(foundCustomer.getId() + " " + foundCustomer.getName());   
   System.out.println(foundCustomer.getAddress().getTown());   
   System.out.println(foundCustomer.getAccounts().get(0).getAccountName() + "\n");   
  }
  
  // find by customer name, address number and account name
  System.out.println("\nSPECIFIC CUSTOMERS:");  
  List<Customer> specficCustomers = customerService.findSpecificCustomers(
    "Mr Customer","101","Business Account");     
  for (Customer foundCustomer : specficCustomers) {
   System.out.println(foundCustomer.getId() + " " + foundCustomer.getName());   
   System.out.println(foundCustomer.getAddress().getTown());   
   System.out.println(foundCustomer.getAccounts().get(0).getAccountName() + "\n");   
  }
  
 } 
 
}

The output from the above would look similiar to the below:

04-Oct-2012 13:48:48 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@15eb0a9: startup date [Thu Oct 04 13:48:48 BST 2012]; root of context hierarchy
04-Oct-2012 13:48:48 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring/applicationContext.xml]
04-Oct-2012 13:48:48 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1c92535: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,customerService,mongo,mongoTemplate,customerRepository,org.springframework.data.repository.core.support.RepositoryInterfaceAwareBeanPostProcessor#0]; root of factory hierarchy

ALL CUSTOMERS:
506d85b115503d4c92392c79 Mr Bank Customer
City
Personal Account

506d85b115503d4c92392c7a Mr Customer
Town
Business Account


SPECIFIC CUSTOMERS:
506d85b115503d4c92392c7a Mr Customer
Town
Business Account

This is a brief overview of Spring Data from MongoDB but there are many other facets to this project including MappingConverters, Compound Indexes and MVC support. For more info http://static.springsource.org/spring-data/data-mongodb/docs/current/reference/html/

Using Morphia to map Java objects in MongoDB

MongoDB is an open source document-oriented NoSQL database system which stores data as JSON-like documents with dynamic schemas.  As it doesn't store data in tables as is done in the usual relational database setup, it doesn't map well to the JPA way of storing data. Morphia is an open source lightweight type-safe library designed to bridge the gap between the MongoDB Java driver and domain objects. It can be an alternative to SpringData if you're not using the Spring Framework to interact with MongoDB.

This post will cover the basics of persisting and querying entities along the lines of JPA by using Morphia and a MongoDB database instance.

There are four POJOs this example will be using. First we have BaseEntity which is an abstract class containing the Id and Version fields:

package com.city81.mongodb.morphia.entity;

import org.bson.types.ObjectId;
import com.google.code.morphia.annotations.Id;
import com.google.code.morphia.annotations.Property;
import com.google.code.morphia.annotations.Version;

public abstract class BaseEntity {

    @Id
    @Property("id")
    protected ObjectId id;

    @Version 
    @Property("version")
    private Long version;

    public BaseEntity() {
        super();
    }

    public ObjectId getId() {
        return id;
    }

    public void setId(ObjectId id) {
        this.id = id;
    }

    public Long getVersion() {
        return version;
    }

    public void setVersion(Long version) {
        this.version = version;
    }

}

Whereas JPA would use @Column to rename the attribute, Morphia uses @Property. Another difference is that @Property needs to be on the variable whereas @Column can be on the variable or the get method.

The main entity we want to persist is the Customer class:

package com.city81.mongodb.morphia.entity;

import java.util.List;
import com.google.code.morphia.annotations.Embedded;
import com.google.code.morphia.annotations.Entity;

@Entity
public class Customer extends BaseEntity {

    private String name;
    private List<Account> accounts;
    @Embedded
    private Address address;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Account> getAccounts() {
        return accounts;
    }

    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

}

As with JPA, the POJO is annotated with @Entity. The class also shows an example of @Embedded:

The Address class is also annotated with @Embedded as shown below:

package com.city81.mongodb.morphia.entity;

import com.google.code.morphia.annotations.Embedded;

@Embedded
public class Address {

    private String number;
    private String street;
    private String town;
    private String postcode;

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    public String getTown() {
        return town;
    }

    public void setTown(String town) {
        this.town = town;
    }

    public String getPostcode() {
        return postcode;
    }

    public void setPostcode(String postcode) {
        this.postcode = postcode;
    }

}

Finally, we have the Account class of which the customer class has a collection of:

package com.city81.mongodb.morphia.entity;

import com.google.code.morphia.annotations.Entity;

@Entity
public class Account extends BaseEntity {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

The above show only a small subset of what annotations can be applied to domain classes. More can be found at http://code.google.com/p/morphia/wiki/AllAnnotations

The Example class shown below goes through the steps involved in connecting to the MongoDB instance, populating the entities, persisting them and then retrieving them:

package com.city81.mongodb.morphia;

import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;
import com.city81.mongodb.morphia.entity.Account;
import com.city81.mongodb.morphia.entity.Address;
import com.city81.mongodb.morphia.entity.Customer;
import com.google.code.morphia.Datastore;
import com.google.code.morphia.Key;
import com.google.code.morphia.Morphia;
import com.mongodb.Mongo;
import com.mongodb.MongoException;

/**
 * A MongoDB and Morphia Example
 *
 */
public class Example {

    public static void main( String[] args ) throws UnknownHostException, MongoException {

     String dbName = new String("bank");
     Mongo mongo = new Mongo();
     Morphia morphia = new Morphia();
     Datastore datastore = morphia.createDatastore(mongo, dbName);       

     morphia.mapPackage("com.city81.mongodb.morphia.entity");
        
     Address address = new Address();
     address.setNumber("81");
     address.setStreet("Mongo Street");
     address.setTown("City");
     address.setPostcode("CT81 1DB");  

     Account account = new Account();
     account.setName("Personal Account");

     List<Account> accounts = new ArrayList<Account>();
     accounts.add(account);  

     Customer customer = new Customer();
     customer.setAddress(address);
     customer.setName("Mr Bank Customer");
     customer.setAccounts(accounts);
    
     Key<Customer> savedCustomer = datastore.save(customer);    
     System.out.println(savedCustomer.getId());

}

Executing the first few lines will result in the creation of a Datastore. This interface will provide the ability to get, delete and save objects in the 'bank' MongoDB instance.

The mapPackage method call on the morphia object determines what objects are mapped by that instance of Morphia. In this case all those in the package supplied. Other alternatives exist to map classes, including the method map which takes a single class (this method can be chained as the returning object is the morphia object), or passing a Set of classes to the Morphia constructor.

After creating instances of the entities, they can be saved by calling save on the datastore instance and can be found using the primary key via the get method. The output from the Example class would look something like the below:

11-Jul-2012 13:20:06 com.google.code.morphia.logging.MorphiaLoggerFactory chooseLoggerFactory
INFO: LoggerImplFactory set to com.google.code.morphia.logging.jdk.JDKLoggerFactory
4ffd6f7662109325c6eea24f
Mr Bank Customer

There are many other methods on the Datastore interface and they can be found along with the other Javadocs at http://morphia.googlecode.com/svn/site/morphia/apidocs/index.html

An alternative to using the Datastore directly is to use the built in DAO support. This can be done by extending the BasicDAO class as shown below for the Customer entity:

package com.city81.mongodb.morphia.dao;

import com.city81.mongodb.morphia.entity.Customer;
import com.google.code.morphia.Morphia;
import com.google.code.morphia.dao.BasicDAO;
import com.mongodb.Mongo;

public class CustomerDAO extends BasicDAO<Customer, String> {    

    public CustomerDAO(Morphia morphia, Mongo mongo, String dbName) {        
        super(mongo, morphia, dbName);    
    }

}

To then make use of this, the Example class can be changed (and enhanced to show a query and a delete):

...

     CustomerDAO customerDAO = new CustomerDAO(morphia, mongo, dbName);
     customerDAO.save(customer);

     Query<Customer> query = datastore.createQuery(Customer.class);
     query.and(        
       query.criteria("accounts.name").equal("Personal Account"),      
       query.criteria("address.number").equal("81"),        
       query.criteria("name").contains("Bank")
     );       

     QueryResults<Customer> retrievedCustomers =  customerDAO.find(query);   

     for (Customer retrievedCustomer : retrievedCustomers) {
         System.out.println(retrievedCustomer.getName());    
         System.out.println(retrievedCustomer.getAddress().getPostcode());    
         System.out.println(retrievedCustomer.getAccounts().get(0).getName());
         customerDAO.delete(retrievedCustomer);
     }  
    
...

With the output from running the above shown below:

11-Jul-2012 13:30:46 com.google.code.morphia.logging.MorphiaLoggerFactory chooseLoggerFactory
INFO: LoggerImplFactory set to com.google.code.morphia.logging.jdk.JDKLoggerFactory
Mr Bank Customer
CT81 1DB
Personal Account

This post only covers a few brief basics of Morphia but shows how it can help bridge the gap between JPA and NoSQL.